Wide adoption of mobile devices along with ubiquitous cellular data coverage has resulted in an explosive growth of mobile applications that expect always-accessible wireless networking. This explosion has placed strains on resources that are scarce in the mobile world: handheld battery life and cellular network capacity. On the user side, poor battery life due to non-optimized mobile apps has been blamed for user dissatisfaction and phone returns. On the network side, the growth rate of mobile data is outstripping the rate at which new cellular wireless capacity is being added, leading to proposals for optimization of data use through techniques such as WI-FI offloading.